WO2016038438A1 - Batterie rechargeable à électrolyte non aqueux - Google Patents

Batterie rechargeable à électrolyte non aqueux Download PDF

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Publication number
WO2016038438A1
WO2016038438A1 PCT/IB2015/001493 IB2015001493W WO2016038438A1 WO 2016038438 A1 WO2016038438 A1 WO 2016038438A1 IB 2015001493 W IB2015001493 W IB 2015001493W WO 2016038438 A1 WO2016038438 A1 WO 2016038438A1
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WIPO (PCT)
Prior art keywords
layer
mass
positive electrode
lfp
ratio
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PCT/IB2015/001493
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English (en)
Inventor
Hideyuki SAKA
Keiichi Takahashi
Hideaki Fujita
Tatsuya Hashimoto
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Toyota Jidosha Kabushiki Kaisha
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Application filed by Toyota Jidosha Kabushiki Kaisha filed Critical Toyota Jidosha Kabushiki Kaisha
Priority to US15/508,765 priority Critical patent/US10243196B2/en
Priority to CN201580047762.XA priority patent/CN106663774B/zh
Priority to DE112015004095.1T priority patent/DE112015004095T5/de
Priority to KR1020177006267A priority patent/KR101917265B1/ko
Publication of WO2016038438A1 publication Critical patent/WO2016038438A1/fr

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/364—Composites as mixtures
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/50—Current conducting connections for cells or batteries
    • H01M50/572—Means for preventing undesired use or discharge
    • H01M50/574—Devices or arrangements for the interruption of current
    • H01M50/578—Devices or arrangements for the interruption of current in response to pressure
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2200/00—Safety devices for primary or secondary batteries
    • H01M2200/20—Pressure-sensitive devices
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to a nonaqueous electrolyte secondary battery.
  • JP 2008-235150 A discloses a nonaqueous electrolyte secondary battery in which a positive electrode active material contains: a lithium-containing metal oxide containing at least Co; and Li b FeP0 4 (wherein b satisfies a condition of 0 ⁇ b ⁇ l).
  • the positive electrode active material such as LiNi 0 .8oCo 0 . 15 Alo.o 5 0 2 is mixed with 10 mass% or less of lithium iron phosphate having a lower action potential than LiNi 0 . 80 Coo.i 5 Alo.o 5 0 2 .
  • an abrupt increase in the resistance of the positive electrode active material at a late stage of discharge that is, low SOC
  • high output can be obtained over a wide range of SOC.
  • there is room for further improvement in such a technique in consideration of the behavior of a battery during overcharge.
  • a large-sized battery for a vehicle may include a pressure-operated current interrupt device (hereinafter, referred to as "CID") that physically interrupts a conductive path when an internal pressure of the battery during overcharge exceeds a predetermined pressure (also referred to as “working pressure”).
  • a positive electrode is required to have a function of causing a reaction with a gas producing agent (also referred to as “overcharge additive”), which is contained in an electrolytic solution or the like, to produce gas such that the CID is rapidly operated during overcharge.
  • a gas producing agent also referred to as “overcharge additive”
  • lithium iron phosphate which is used as the positive electrode active material having a low action potential has significantly low conductivity. Therefore, this low conductivity is compensated for by coating surfaces of lithium iron phosphate particles with carbon. Further, in order to secure a predetermined battery output, it is necessary to increase a ratio of a conductive material in a positive electrode mixture into which lithium iron phosphate is mixed. Moreover, lithium iron phosphate has low capacity per volume. Therefore, the positive electrode capacity per volume decreases depending on the mixing amount of lithium iron phosphate. Accordingly, in order to maintain the battery capacity, it is necessary to improve the filling factor, that is, the mixture density of a positive electrode mixture layer depending on the mixing amount of lithium iron phosphate.
  • the present invention provides a nonaqueous electrolyte secondary battery in which the output in a low SOC is high, and the amount of gas produced during overcharge is large.
  • a nonaqueous electrolyte secondary battery including: a pressure-operated current interrupt device; a nonaqueous electrolytic solution containing a gas producing agent; and an electrode group in which a positive electrode and a negative electrode are arranged to face each other with a separator interposed between the positive electrode and the negative electrode.
  • the positive electrode includes a positive electrode current collector and a positive electrode mixture layer that has a main surface and is formed on the positive electrode current collector.
  • the positive electrode mixture layer includes a first layer that includes the main surface and a second layer that is formed closer to the positive electrode current collector side than the first layer. A ratio of the volume of the first layer to the volume of the positive electrode mixture layer is 20 vol% to 75 vol%.
  • the first layer contains lithium iron phosphate and lithium nickel cobalt manganese composite oxide.
  • a ratio of the mass of the lithium iron phosphate to the total mass of the lithium iron phosphate and the lithium nickel cobalt manganese composite oxide in the first layer is more than 0 mass% and 80 mass% or less.
  • the second layer contains lithium nickel cobalt manganese composite oxide.
  • a ratio of the mass of the lithium iron phosphate to the total mass of the positive electrode active material in the positive electrode mixture layer is 7.5 mass% to 20 mass%.
  • a maximum pore size of the first layer is 0.50 ⁇ to 0.70 ⁇ .
  • the positive electrode mixture layer has a two-layer structure including: a second layer (lower layer) containing NCM; and a first layer (upper layer) containing LFP and NCM. That is, LFP is biasedly distributed on the surface of the positive electrode mixture layer.
  • the positive electrode mixture layer during charging a reaction of releasing lithium ions (Li + ) is initiated from the surface portion close to the negative electrode. Therefore, in the positive electrode mixture layer during charging, a Li + concentration gradient is generated in a thickness direction thereof, and thus concentration polarization occurs in the vicinity of the surface.
  • the first layer containing LFP is formed on the surface portion. Since LFP is a positive electrode active material having low conductivity (that is, high resistance) as described above, resistance polarization is likely to occur in the first layer. A combination of these polarizations causes a increase of positive electrode potential in a local portion of the first layer.
  • the positive electrode mixture layer contains LFP. As a result, it is considered that, even when the mixture density of the positive electrode mixture layer is somewhat high, it is difficult to decrease the amount of gas produced.
  • the first layer includes the main surface of the positive electrode mixture layer. Therefore, the first layer is in contact with the separator.
  • the separator has a higher porosity than the positive electrode mixture layer. Therefore, an abundant amount of the nonaqueous electrolytic solution containing the gas producing agent is stored in the separator. Therefore, even when the gas producing agent is consumed due to the gas production reaction in the first layer, the gas producing agent is supplied from the separator to the first layer along with the nonaqueous electrolytic solution, and the gas production reaction can be continued without the depletion of the gas producing agent in the first layer. In this way, in the above-described nonaqueous electrolyte secondary battery, a predetermined amount of gas can be secured early during overcharge.
  • the ratio of the mass of LFP to the total mass of the positive electrode active material in the entire positive electrode mixture layer is less than 7.5 mass%, a desired output may not be obtained in a low SOC.
  • the mass ratio of LFP is more than 20 mass%, a balance between the output in a low SOC and the other characteristics (for example, charging-discharging cycle characteristics) may not be maintained.
  • the ratio of the mass of LFP to the total mass of the positive electrode active material is limited to be 7.5 mass% to 20 mass%.
  • the ratio of the volume of the first layer to the volume of the positive electrode mixture layer is limited to be 20 vol% to 75 vol%.
  • the reason why the volume ratio of the first layer is adjusted to be 20 vol% or more is as follows: when the volume ratio of the first layer, which is a main reaction field of the gas production reaction, is less than 20 vol%, the amount of gas produced may decrease.
  • the reason why the volume ratio of the first layer is adjusted to be 75 vol% or less is as follows: when the volume ratio of the first layer is more than 75 vol%, a difference from a state where LFP is uniformly distributed over the entire positive electrode mixture layer (related art) can be reduced.
  • the binder is a resistance component, which may cause a decrease in output. Therefore, in the above-described nonaqueous electrolyte secondary battery, the ratio of the mass of LFP to the total mass of LFP and NCM in the first layer is limited to be 80 mass% or less. As a result, the generation of strain can be prevented, and a decrease in capacity caused by charging-discharging cycles can be prevented.
  • a maximum pore size of the first layer is 0.50 ⁇ to 0.70 ⁇ .
  • gas produced from the first layer can be easily discharged, and the internal pressure can be efficiently increased.
  • the area of the lithium iron phosphate may be 8.6 m /g to 13.2 m /g.
  • the BET specific surface area of LFP may be 8.6 m /g to 13.2 m /g.
  • the output in a low SOC can be improved.
  • the BET specific surface area of LFP to be 13.2 m 2 /g or less, the maximum pore size of the first layer can be easily controlled to be 0.50 ⁇ or more.
  • BET specific surface area refers to the specific surface area measured using a BET method.
  • the BET specific surface area can be measured using a general specific surface area measuring device (for example, "Macsorb
  • the maximum pore size of the positive electrode mixture layer (first layer) can be measured by mercury intrusion porosimetry using a pore distribution measuring device (for example, "Autopore IV
  • a ratio of the mass of a conductive material to the mass of the first layer may be 5 mass% to 15 mass%.
  • a ratio of the mass of a conductive material to the mass of the second layer may be 3 mass% to 11 mass%.
  • a mixture density of the positive electrode mixture layer may be 2.5 g/cm 3 to 3.5 g/cm 3 .
  • a nonaqueous electrolyte secondary battery can be provided in which the output in a low SOC is high, and the amount of gas produced during overcharge is large.
  • FIG 1 is a schematic diagram showing a configuration example of a nonaqueous electrolyte secondary battery according to an embodiment of the invention
  • FIG. 2 is a schematic cross-sectional view taken along line II-II of FIG 1 ;
  • FIG 3 is a schematic diagram showing a configuration example of an electrode group according to the embodiment of the invention.
  • FIG. 4 is a schematic diagram showing a configuration example of a positive electrode according to the embodiment of the invention.
  • FIG 5 is a schematic cross-sectional view taken along line V-V of FIG 4; and FIG. 6 is a schematic diagram showing a configuration example of a negative electrode according to the embodiment of the invention.
  • FIG 7 is a table showing properties of positive electrode active material according to the embodiment of the invention and properties of positive electrode active material according to the comparative example.
  • FIG. 8 is a table showing evaluation of the respective batteries and the respective positive electrodes according to the embodiment of the invention and evaluation of the respective batteries and the respective positive electrodes according to the comparative example.
  • FIG 9 is a table showing physical properties of each LFP powder according to the embodiment of the invention.
  • FIG. 10 is a table showing the configurations of the positive electrode mixture layers in the batteries Al 0 to Al 5 according to the embodiment of the invention.
  • FIG 11 is a table showing the output in a low SOC, the amount of gas produced during overcharge, and charging-discharging cycle characteristics of the batteries A10 to A15 according to the embodiment of the invention.
  • FIG. 1 is a schematic diagram showing a configuration example of a nonaqueous electrolyte secondary battery according to the embodiment.
  • the battery 100 is a sealed battery and includes a square external body 50.
  • the external body 50 includes a bottomed square case 52 and a lid 54.
  • the external body 50 is formed of, for example, an aluminum (Al) alloy.
  • the case 52 and the lid 54 are joined to each other by, for example, laser welding.
  • a positive electrode terminal 70 and a negative electrode terminal 72 are provided on the lid 54.
  • a safety valve 55 is adjusted to be opened under a higher pressure than a working pressure of a CID 30 described below.
  • FIG. 2 is a schematic cross-sectional view showing the battery 100 taken along line II-II of FIG. 1.
  • the battery 100 includes an electrode group 80 and a nonaqueous electrolytic solution (not shown).
  • the inside of the battery 100 is not completely filled with the above components, and a space volume is present therein.
  • space volume refers to the volume obtained by subtracting the volume of the components (the electrode group 80, the nonaqueous electrolytic solution, and the like) from the internal volume of the external body 50.
  • the embodiment is particularly effective for a large-sized battery having a large space volume therein. This is because, as the space volume increases, the amount of gas required to operate the CID 30 increases.
  • Examples of the large-sized battery include batteries (having a rated capacity of about 20 Ah or higher) which are used in a hybrid vehicle (HV), an electric vehicle (EV), and the like.
  • the pressure-operated CID 30 is arranged on a conductive path on the positive electrode side of the battery 100.
  • the CID 30 includes a deformed metal plate 32, a connection metal plate 34, and an insulating case 38.
  • the connection metal plate 34 is electrically connected to a positive electrode current collector plate 74.
  • the deformed metal plate 32 has a curved portion 33 whose center is curved downward and is joined to the connection metal plate 34 at a tip end (junction 36) of the curved portion 33.
  • the deformed metal plate 32 is electrically connected to the positive electrode terminal 70 through a current collector lead 35. In this way, a conductive path which connects the positive electrode terminal 70 and the positive electrode current collector plate 74 to each other is formed.
  • the insulating case 38 is formed of, for example, a resin, is arranged to surround the deformed metal plate 32, seals a space surrounded by the deformed metal plate 32, the insulating case 38, and the external body 50, and separates the above space from the other spaces inside the external body 50.
  • the internal pressure of the external body 50 increases, the internal pressure acts on a bottom surface of the curved portion 33 of the deformed metal plate 32 such that the curved portion 33 is pushed up.
  • the internal pressure exceeds the working pressure the curved portion 33 is flipped upside down, the junction 36 is disconnected from the positive electrode current collector plate 74, and the conductive path which connects the positive electrode terminal 70 and the positive electrode current collector plate 74 to each other is interrupted.
  • the CID 30 is provided on the conductive path on the positive electrode side.
  • the CID may be provided on a conductive path on the negative electrode side or on both the conductive paths.
  • the CID is not limited to the above-described configuration and may have any configuration as long as the CID operates in response to an increase in the internal pressure. For example, when a value of the internal pressure detected by a sensor exceeds a set value, an external circuit which interrupts the current may be set as the CID.
  • FIG. 3 is a schematic diagram showing a configuration example of the electrode group.
  • the electrode group 80 is a wound electrode group.
  • a positive electrode 10, a negative electrode 20, and separators 40 constituting the electrode group 80 are elongated belt-shaped sheet members.
  • the positive electrode 10 and the negative electrode 20 are arranged to face each other with the separators 40 interposed therebetween, and the electrode group 80 is wound in a longitudinal direction of the respective members.
  • Each of the positive electrode 10 and the negative electrode 20 has an exposure portion EP where a current collector (typically, metal foil) is exposed at an end portion on one side in a width direction (transverse direction).
  • a current collector typically, metal foil
  • the positive electrode 10 and the negative electrode 20 are arranged to face each other such that the exposure portions EP protrude in different directions on a winding axis AW.
  • the exposure portions EP of the electrode group 80 are welded to the positive electrode current collector plate 74 and the negative electrode current collector plate 76, respectively.
  • the positive electrode current collector plate 74 is connected to the positive electrode terminal 70 through the CID 30, and the negative electrode current collector plate 76 is connected to the negative electrode terminal 72.
  • a positive electrode mixture layer 12 includes a first layer 12a and a second layer 12b. As a result, a large amount of gas is produced during overcharge, and the CID 30 can be operated early.
  • FIG 4 is a schematic diagram showing a configuration example of the positive electrode 10.
  • the positive electrode 10 includes an elongated belt-shaped positive electrode current collector 11 and an elongated belt-shaped positive electrode mixture layer 12 that is formed on opposite main surfaces of the positive electrode current collector 11.
  • the positive electrode current collector 11 is formed of, for example, Al foil.
  • the positive electrode 10 can be manufactured using a method of the related art. For example, using a die coater, a positive electrode mixture paste obtained by dispersing a positive electrode mixture in a predetermined solvent is applied to the opposite main surfaces of the positive electrode current collector 11 and is dried. As a result, the positive electrode 10 can be manufactured.
  • the solvent for example, N-methyl-2-pyrrolidone (NMP) can be used as the solvent.
  • NMP N-methyl-2-pyrrolidone
  • the dried positive electrode mixture layer 12 may be pressed using a rolling mill or the like to adjust the thickness and the mixture density thereof.
  • the mixture density of the positive electrode mixture layer 12 is, for example, 2.5 g/cm 3 to 3.5 g/cm 3 .
  • the positive electrode mixture layer 12 includes a main surface MS.
  • FIG. 5 is a schematic cross- sectional view taken along line V-V of FIG. 4.
  • the positive electrode mixture layer 12 includes: the first layer 12a that includes the main surface MS; and the second layer 12b that is formed closer to the positive electrode current collector 11 side than the first layer 12a.
  • the first layer 12a contains LFP 1 and NCM 2
  • the second layer 12b contains the NCM 2.
  • This two-layer structure can be formed, for example, using a method including: applying a positive electrode mixture paste for forming the second layer 12b to the main surface of the positive electrode current collector 11 and drying the positive electrode mixture paste; and applying a positive electrode mixture paste for forming the first layer 12a to the second layer 12b and drying the positive electrode mixture paste.
  • the positive electrode mixture layer 12 consists of only the first layer 12a and the second layer 12b.
  • the positive electrode mixture layer 12 may further include another layer within a range where the amount of gas produced during overcharge and the output in a low SOC are not excessively decreased.
  • a conductive layer containing a conductive material and a binder may be formed between the first layer 12a and the second layer 12b or between the second layer 12b and the positive electrode current collector 11.
  • the first layer 12a contains the LFP 1 and the NCM 2 as the positive electrode active material and further contains a conductive material and a binder (both of which are not shown).
  • a ratio of the mass of the positive electrode active material to the mass of the first layer 12a is, for example, 80 mass% to 95 mass%, preferably 80 mass% to 90 mass%, and more preferably 85 mass% to 90 mass%.
  • a ratio (volume ratio) of the volume of the first layer 12a to the volume of the positive electrode mixture layer 12 is 20 vol% to 75 vol%.
  • the volume ratio of the first layer 12a is less than 20 vol%, portions where the polarizations occur cannot be sufficiently secured, and the amount of gas produced may decrease.
  • the volume ratio of the first layer 12a is more than 75 vol%, resistance polarization decreases, and the amount of gas produced may decrease. From the viewpoints of further increasing the amount of gas produced and further improving the output in a low SOC, the volume ratio of the first layer 12a is preferably 20 vol% to 50 vol% and more preferably 25 vol% to 50 vol%.
  • the application area of the first layer 12a (the area of the main surface MS) is substantially the same as the application area of the second layer 12b.
  • the reason is as follows. When these areas are significantly different from each other, the mixture density may be non-uniform in a portion of the positive electrode mixture layer 12, which may decrease charging-discharging cycle characteristics.
  • the application areas are substantially the same implies that the application area of the first layer 12a is 0.97 times to 1.03 times the application area of the second layer 12b.
  • the above-described ratio of the volume of the first layer 12a to the volume of the positive electrode mixture layer 12 can be calculated based on a thickness Tl of the first layer 12a and a thickness T2 of the second layer 12b. That is, the ratio of the volume of the first layer 12a to the volume of the positive electrode mixture layer 12 can be calculated in a percentage from T1/(T1+T2).
  • the thickness (T1+T2) of the positive electrode mixture layer 12 is, for example, 40 ⁇ to 100 ⁇ .
  • the maximum pore size of the first layer 12a is 0.5 ⁇ or more. As a result, gas produced from the first layer 12a can be easily discharged, and the internal pressure can be efficiently increased during overcharge. According to experiment results described below, the maximum pore size of the first layer 12a is more preferably 0.53 ⁇ or more and still more preferably 0.64 ⁇ or more. As described below, the maximum pore size of the first layer 12a can be controlled, for example, by adjusting the BET specific surface area of the LFP 1 contained in the first layer 12a. That is, as the BET specific surface area of LFP powder is decreased, the size of pores contained in the first layer 12a can be increased. However, when the BET specific surface area is excessively small, the intercalation reaction of Li + is less likely to occur, and output characteristics may decrease. From this point of view, the maximum pore size is 0.70 ⁇ or less.
  • the first layer 12a contains particulate lithium iron phosphate (LFP 1).
  • LFP is a complex phosphate represented by the chemical formula LiFeP0 4 and has an olivine type crystal structure. LFP is capable of intercalation and deintercalation of Li+ at 3.3 V to 3.4 V (vs. Li + /Li).
  • the above-described value of 3.3 V to 3.4 V corresponds to about 20% (low SOC) in terms of the SOC of the battery.
  • the Li + concentration in LFP is still low, and LFP can intercalate Li + .
  • LFP is present in the surface (that is, the first layer 12a including the main surface MS) of the positive electrode mixture layer 12. Therefore, Li + supplied from the outside of the positive electrode mixture layer 12 can easily reach LFP. In this way, it is considered that high output can be exhibited in a low SOC.
  • LiFeP04 representing LFP
  • a portion of Fe may be substituted with another element (for example, Co, Ni, or Mn) within a range where an increase in potential during overcharge and the output in a low SOC do not excessively deteriorate.
  • LFP may be doped with a small amount of different element.
  • the different element include magnesium (Mg), silicon (Si), calcium (Ca), titanium (Ti), vanadium (V), chromium (Cr), zinc (Zn), gallium (Ga), zirconium (Zr), niobium (Nb), molybdenum (Mo), tin (Sn), hafnium (Hi), and tungsten (W).
  • the surface of LFP is coated with carbon or the like because the conductivity of LFP is compensated for and output characteristics are further improved.
  • a carbon source for example, a heavy aromatic residue (pitch) obtained from petrochemical process or a carbohydrate
  • Pitch heavy aromatic residue
  • C carbon
  • the coating amount of carbon is not particularly limited.
  • a mass ratio (LFP:C) of the matrix (LFP) to carbon (C) is 98:2 to 99: 1.
  • the BET specific surface area of LFP is preferably 8.6 m 2 /g to 13.2 m 2 /g.
  • the BET specific surface area is preferably 8.6 m 2 /g to 13.2 m 2 /g.
  • the BET specific surface area of the LFP powder is more preferably 8.6 m 2 /g to 11.6 m 2 /g and still more preferably 8.6 m 2 /g to 9.5 m 2 /g.
  • the BET specific surface area of LFP can be adjusted, for example, by adjusting temperature conditions during the firing of the precursor of LFP.
  • D50 of LFP is, for example, 5.0 ⁇ to 15.0 ⁇ , preferably 7.5 ⁇ to 14.0 ⁇ , more preferably 8.4 ⁇ to 12.9 ⁇ , and still more preferably 8.4 ⁇ to 9.5 ⁇ .
  • D50 refers to a particle size corresponding to an cumulative value of 50% in a particle size distribution obtained using a laser diffraction scattering method.
  • D10 and D90 refer to particle sizes corresponding to a cumulative value of 10% and a cumulative value of 90% in the same particle size distribution, respectively.
  • the first layer 12a contains particulate lithium nickel cobalt manganese composite oxide (NCM 2).
  • NCM may be doped with a small amount of the above-described different element (for example, Mg).
  • binder of secondary particles is, for example, 1 ⁇ to 20 ⁇ , preferably 3 ⁇ to 15 ⁇ , and more preferably 5 ⁇ to 10 ⁇ .
  • a ratio of the mass of LFP to the total mass of LFP and NCM in the first layer 12a is more than 0 mass% to 80 mass%.
  • the mass ratio of LFP is more than 80 mass%, strain is generated between the first layer 12a and the second layer 12b, which may decrease charging-discharging cycle characteristics.
  • the ratio of the mass of LFP to the total mass of LFP and NCM in the first layer 12a is preferably 50 mass% or less, more preferably 40 mass% or less, and still more preferably 30 mass% or less.
  • the ratio of the mass of LFP to the total mass of LFP and NCM in the first layer 12a is preferably 5 mass% or more, more preferably 10 mass% or more, and still more preferably 15 mass% or more.
  • the conductive material a material of the related art can be used.
  • one or more materials selected from acetylene black (AB), Ketjen black (registered trade name), flaky graphite, lump graphite, amorphous graphite, and vapor-grown carbon fiber (VGCF) can be used.
  • the mass ratio of the conductive material is set to be high.
  • a ratio of the mass of the conductive material to the mass of the first layer 12a is, for example, 5 mass% to 15 mass%, preferably 7 mass% to 13 mass%, and more preferably 9 mass% to 11 mass%.
  • binder a material of the related art can be used.
  • PVdF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • a ratio of the mass of the binder to the mass of the first layer 12a is, for example, 1 mass% to 7 mass% and preferably 2 mass% to 6 mass%.
  • the second layer 12b is formed closer to the positive electrode current collector 11 side than the first layer 12a.
  • the second layer 12b contains NCM as the positive electrode active material and further contains a conductive material and a binder.
  • the second layer 12b may contain a smaller amount of LFP than the first layer 12a.
  • NCM contained in the first layer 12a is not necessarily the same as NCM contained in the second layer 12b.
  • a ratio of the mass of the positive electrode active material to the mass of the second layer 12b is, for example, 85 mass% to 95 mass%, preferably 87 mass% to 93 mass%, and more preferably 88 mass% to 92 mass%.
  • the second layer 12b also contains the conductive material and the binder described above in addition to the positive electrode active material (NCM).
  • the second layer 12b does not contain LFP or contains a smaller amount of LFP than the first layer 12a. Therefore, in the second layer 12b, the mass ratio of the conductive material can be set to be low.
  • a ratio of the mass of the conductive material to the mass of the second layer 12b is, for example, 3 mass% to 11 mass%, preferably 4 mass% to 10 mass%, and more preferably 5 mass% to 9 mass%.
  • a ratio of the mass of the binder to the mass of the second layer 12b is, for example, 1 mass% to 5 mass% and preferably 2 mass% to 4 mass%.
  • a ratio of the mass of LFP to the total mass of the positive electrode active material in the entire positive electrode mixture layer 12 is 7.5 mass% to 20 mass%.
  • the mass ratio of LFP is less than 7.5 mass%, a desired output may not be obtained in a low SOC.
  • the mass ratio of LFP is more than 20 mass%, a balance between the output in a low SOC and charging-discharging cycle characteristics may not be maintained. From this point of view, the mass ratio of LFP is preferably 7.5 mass% to 15 mass% and more preferably 10 mass% to 15 mass%.
  • the positive electrode mixture layer 12 may further contain another positive electrode active material (for example, LiCo0 2 , LiNi0 2 , or LiMn 2 0 4 ) in addition to LFP and NCM.
  • another positive electrode active material for example, LiCo0 2 , LiNi0 2 , or LiMn 2 0 4
  • a ratio of the mass of the other positive electrode active material to the total mass of the positive electrode active materials is set to be less than 50 mass% because a balance between the output in a low SOC and the amount of gas produced during overcharge can be maintained. Due to the same reason, the mass ratio of the other positive electrode active material is set to be more preferably less than 30 mass%, still more preferably less than 10 mass%, and most preferably 0 mass%.
  • FIG 6 is a schematic diagram showing a configuration example of the negative electrode 20.
  • the negative electrode 20 includes an elongated belt-shaped negative electrode current collector 21 and an elongated belt-shaped negative electrode mixture layer 22 that is formed on opposite main surfaces of the negative electrode current collector 21.
  • the negative electrode current collector 21 is formed of, for example, Cu foil.
  • the negative electrode 20 can be manufactured using a method of the related art. For example, using a die coater, a negative electrode mixture paste obtained by dispersing a negative electrode mixture in a predetermined solvent is applied to the opposite main surfaces of the negative electrode current collector 21 and is dried. As a result, the negative electrode 20 can be manufactured.
  • the solvent for example, water (including ion exchange water) can be used.
  • the dried negative electrode mixture layer 22 may be pressed using a rolling mill or the like to adjust the thickness and the mixture density thereof.
  • the mixture density of the negative electrode mixture layer 22 is, for example, 0.5 g/cm 3 to 2.0 g/cm 3 .
  • the negative electrode mixture layer 22 is formed by attaching a negative electrode mixture containing a negative electrode active material, a thickener, and a binder to the main surfaces of the negative electrode current collector 21.
  • the negative electrode active material is not particularly limited, and any material which can function as a negative electrode active material of a nonaqueous electrolyte secondary battery can be used.
  • a carbon negative electrode active material such as graphite or coke, or an alloy negative electrode active material of Si, Sn, and the like can be used.
  • a ratio of the mass of the negative electrode active material to the mass of the negative electrode mixture layer 22 is, for example, 90 mass% to 99 mass%.
  • the thickener and the binder a material of the related art can be used.
  • the thickener for example, carboxymethyl cellulose (CMC) or polyvinyl alcohol (PVA) can be used.
  • the binder for example, styrene-butadiene rubber (SRB) or PTFE can be used.
  • a ratio of the mass of the thickener and the binder to the mass of the negative electrode mixture layer 22 is, for example, 1 mass% to 10 mass%.
  • the separator 40 prevents electrical contact between the positive electrode 10 and the negative electrode 20 while allowing penetration of Li + .
  • a microporous membrane formed of a polyolefin material is preferable from the viewpoints of mechanical strength and chemical stability.
  • a microporous membrane formed of polyethylene (PE), polypropylene (PP), or the like is preferable.
  • plural microporous membranes may be laminated, or a heat resistance layer containing an inorganic filler (for example, alumina particles) may be formed on the surface thereof.
  • the thickness of the separator 40 is, for example, 5 ⁇ to 40 ⁇ .
  • the pore size and porosity of the separator 40 may be appropriately adjusted such that the air permeability is a desired value.
  • the nonaqueous electrolytic solution is obtained by dissolving a Li salt in an aprotic solvent.
  • the aprotic solvent which can be used include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), ⁇ -butyrolactone (yBL), and vinylene carbonate (VC); and chain carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC).
  • a combination of two or more kinds is preferable from the viewpoints of electrical conductivity and electrochemical stability.
  • a mixture of a cyclic carbonate and a chain carbonate is preferably used.
  • a volume ratio of the cyclic carbonate to the chain carbonate is preferably 1 :9 to 5:5.
  • Li salt for example, lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiC104), lithium hexafluoroarsenate (LiAsF 6 ), lithium bis(trifluoromethanesulfonyl)imide (Li(CF 3 S0 2 ) 2 N), or lithium trifluoromethanesulfonate (LiCF 3 S0 3 ) can be used.
  • Li salts a combination of two or more kinds may be used.
  • the concentration of the Li salt in the nonaqueous electrolytic solution is not particularly limited and is preferably 0.5 mol/L to 2.0 mol/L from the viewpoint of improving output characteristics, charging-discharging cycle characteristics, and the like.
  • the nonaqueous electrolytic solution contains a gas producing agent.
  • the gas producing agent is a compound having an oxidation potential in a charge region (hereinafter, referred to as "overcharge region") where the SOC of the battery exceeds 100%.
  • overcharge region a charge region where the SOC of the battery exceeds 100%.
  • the upper limit charge voltage of the battery is 4.0 V to 4.2 V
  • a compound having an oxidation potential of about 4.5 V or higher vs. Li + /Li
  • an aromatic compound such as cyclohexylbenzene (CHB), biphenyl (BP), biphenyl ether (BPE), tert-butylbenzene (TBB), or tert-amylbenzene (TAB), or a derivative thereof can function as the gas producing agent.
  • CHB and BP are particularly preferable because the amount of gas produced is large.
  • These compounds starts electrolytic polymerization to produce a polymerization product when the positive electrode potential exceeds the oxidation potential thereof.
  • This polymerization product increases the battery resistance and produces gas such that an increase in the internal pressure is accelerated.
  • the mechanism of the gas production is not limited to the above configuration. As long as gas is produced in the overcharge region, any mechanism may be used to produce gas.
  • the gas producing agent not only one kind but also a combination of two or more kinds may be used. However, from the viewpoint of increasing the amount of gas produced, it is preferable that the gas producing agent contains CHB. Therefore, when a combination of two or more kinds is used, it is preferable that the composition thereof is selected such that a ratio of the mass of CHB to the total mass of the gas producing agent is 50 mass% or more. For example, CHB and BP having the same mass can be added to the nonaqueous electrolytic solution to function as the gas producing agent. The ratio of the mass of CHB to the total mass of the gas producing agent is more preferably 70 mass% or more and still more preferably 90 mass% or more.
  • the content of the gas producing agent in the nonaqueous electrolytic solution (that is, the addition amount of the gas producing agent to the nonaqueous electrolytic solution) is preferably 1 mass% to 7 mass%.
  • the content of the gas producing agent is more preferably 2 mass% to 5 mass% because the production cost can be reduced while securing a large amount of gas produced.
  • the embodiment is not limited to the square battery and may be applied to a cylindrical battery or a laminate battery (also referred to as "pouch type battery”).
  • the configuration of the electrode group is not limited to the wound type and may be a laminate type (also referred to as "stack type").
  • Experiment 1 Examination on Positive Electrode Mixture Layer>
  • the effects of the layer configuration of the positive electrode mixture layer, the mixing ratio of LFP, and the like on battery performance were examined. Specifically, the following batteries Al to A9 and batteries Bl to B14 were prepared to evaluate the output in a low SOC, the amount of gas produced during overcharge, and charging-discharging cycle characteristics thereof.
  • the batteries Al to A9 correspond to Examples
  • the batteries Bl to B14 correspond to Comparative Examples.
  • Powder of lithium phosphate monohydrate, powder of lithium ferrous dihydrate, and powder of ammonium dihydrogen phosphate were prepared. These powders were mixed with each other in the same molar amount to prepare a precursor of LFP. Further, a carbon source (glucose) was added to the precursor, was fired at 800°C for 12 hours, and was crushed to obtain LFP powder.
  • this LFP powder will be referred to as "LFP (d)".
  • the positive electrode 10 was manufactured which was a sheet member having an elongated belt shape and had the exposure portion EP at an end portion on one side in the width direction.
  • the length Lc of the positive electrode 10 in FIG. 4 was 6150 mm
  • the width Wc of the positive electrode mixture layer 12 was 117 mm
  • the electrode thickness was 120 um.
  • electrode thickness refers to the sum of the thickness of the positive electrode current collector 11 and the thickness of the positive electrode mixture layer 12 that is formed on opposite main surfaces of the positive electrode current collector 11.
  • NCM-only paste Powder of a positive electrode active material (NCM), powder of a conductive material (AB), and powder of a binder (PVdF) were kneaded with a solvent (NMP) to obtain a positive electrode mixture paste (hereinafter, referred to as "NCM-only paste") for forming the second layer 12b.
  • NCM-only paste a positive electrode mixture paste
  • a mixing ratio positive electrode active material: conductive material :binder; mass ratio
  • a positive electrode active material LFP and NCM
  • powder of a conductive material AB
  • powder of a binder PVdF
  • NMP solvent
  • a mixing ratio positive electrode active material: conductive material :binder; mass ratio
  • a ratio of the mass of LFP to the total mass of LFP and NCM was 13.3 mass%.
  • the NCM-only paste was applied to the opposite main surfaces of the positive electrode current collector 11 (Al foil having a thickness of 15 ⁇ ) to have a predetermined coating weight (application mass per unit area) and was dried with hot air. As a result, the second layer 12b was formed. Further, the mixed paste was applied to the second layer 12b to have a predetermined coating weight and was dried with hot air. As a result, the first layer 12a was formed. In this way, the positive electrode mixture layer 12 was formed. Next, the positive electrode mixture layer 12 was pressed such that the mixture density thereof was 3.0 g/cm 3 to obtain the positive electrode 10.
  • the coating weights of the first layer 12a and the second layer 12b were adjusted such that: in the pressed positive electrode mixture layer 12, the volume ratio of the first layer 12a (T1/(T1+T2), which was calculated from the thickness Tl of the first layer 12a and the thickness T2 of the second layer 12b, was the value shown in Table 1 of FIG. 7; and the ratio of the mass of LFP to the total mass of the positive electrode active material in the positive electrode mixture layer 12 was the value shown in Table 1 of FIG 7.
  • the negative electrode 20 was manufactured which was a sheet member having an elongated belt shape and had the exposure portion EP at an end portion on one side in the width direction.
  • the length La of the negative electrode 20 in FIG 6 was 6300 mm
  • the width Wa of the negative electrode mixture layer 22 was 122 mm
  • the electrode thickness was 130 ⁇ .
  • the negative electrode mixture paste was applied to the opposite main surfaces of the negative electrode current collector 21 and was dried with hot air to form the negative electrode mixture layer 22. As a result, the negative electrode 20 was obtained.
  • LiPF6 (1.0 mol/L) was dissolved in a mixed solvent containing EC, DMC, and
  • the separators 40 having a thickness of 24 ⁇ and a three-layer structure in which a PP layer, a PE layer, and a PP layer were laminated in this order were prepared. Referring to FIG. 3, the positive electrode 10 and the negative electrode 20 were wound such that they faced each other with the separators 40 interposed therebetween. As a result, an elliptical electrode group was obtained. Further, the electrode group was pressed in a flat shape to obtain the wound type electrode group 80.
  • the case 52 and the lid 54 were prepared, in which the positive electrode terminal 70, the positive electrode current collector plate 74, the negative electrode terminal 72, and the negative electrode current collector plate 76 were provided on the lid 54 in advance. After the positive electrode current collector plate 74 and the negative electrode current collector plate 76 were connected to the electrode group 80, the electrode group 80 was inserted into the case 52, and the case 52 and the lid 54 were joined to each other by welding.
  • a predetermined amount of nonaqueous electrolytic solution was injected through a liquid injection hole (not shown) provided on the lid 54, and a sealing screw was fastened to the liquid injection hole to seal the inside of the case 52.
  • a nonaqueous electrolyte secondary battery (battery Al) having a rated capacity (design capacity) of 25 Ah was obtained.
  • the batteries A2 to A9 and the batteries B12 and B13 were obtained using the same method as that of the battery Al , except that the ratio of the volume of the first layer 12a to the volume of the positive electrode mixture layer 12, the ratio of the mass of LFP to the total mass of the positive electrode active material in the first layer 12a, and the ratio of the mass of LFP to the total mass of the positive electrode active material in the positive electrode mixture layer 12 were changed as shown in Table 1 of FIG. 7.
  • the batteries Bl and B2 were obtained using the same method as that of the battery Al, except that the NCM-only paste was used, a single-layer positive electrode mixture layer was formed by changing the coating weight such that the battery capacity was the same as that of the battery Al , and the mixture density of the positive electrode mixture layer was adjusted to be the value shown in Table 1 of FIG. 7.
  • Table 1 the above layer configuration of the positive electrode mixture layer is shown as "NCM Single Layer".
  • the battery B3 was obtained using the same method as that of the battery Al, except that a positive electrode mixture paste having a mixing ratio (LFP:NCM:conductive material ibinder; mass ratio) of the positive electrode mixture of 9: 81 :7:3 was used, and a single-layer positive electrode mixture layer was formed by changing the coating weight such that the battery capacity was the same as that of the battery Al .
  • the above layer configuration of the positive electrode mixture layer is shown as "(LFP+NCM) Single-Layer".
  • the (LFP+NCM) single-layer was made assuming a technique of the related art in which LFP was uniformly distributed over the entire positive electrode mixture layer.
  • the batteries B4 and B5 were obtained using the same method as that of the battery B3, except that the ratio of the mass of LFP to the total mass of the positive electrode active material was changed as shown in Table 1 of FIG. 7.
  • the batteries B6 to B10 were obtained using the same method as that of the batteries A2 to A9, except that the ratio of the mass of LFP to the mass of the positive electrode active material in the first layer 12a, and the ratio of the mass of LFP to the total mass of the positive electrode active material in the positive electrode mixture layer 12 were changed as shown in Table 1 of FIG 7.
  • the batteries Bl l and B14 were obtained using the same method as that of the batteries A2 to A9, except that a positive electrode mixture paste having a mixing ratio (LFP conductive material :binder; mass ratio) of the positive electrode mixture of 85:10:5 was used as the positive electrode mixture paste for forming the first layer, and the mixture density of the positive electrode mixture layer was adjusted to be the value shown in Table 1 of FIG 7.
  • a positive electrode mixture paste having a mixing ratio (LFP conductive material :binder; mass ratio) of the positive electrode mixture of 85:10:5 was used as the positive electrode mixture paste for forming the first layer, and the mixture density of the positive electrode mixture layer was adjusted to be the value shown in Table 1 of FIG 7.
  • the unit “C” for the current value refers to the current value at which the rated capacity of a battery is completely discharged in 1 hour.
  • CC refers to the constant current
  • CV refers to the constant voltage
  • CP refers to the constant power.
  • each battery was initially charged and discharged at a current value of 0.2 C in a voltage range of 4.1 V to 3.0 V to obtain the initial capacity of the battery.
  • an amount of electricity corresponding to SOC 20% was applied to the battery based on the initial capacity.
  • a laminate battery was separately prepared according to the following steps [a] to [e] and was evaluated. The results are shown in Table 2 of FIG. 8.
  • [a] A measurement positive electrode having a size of 35 mmx35 mm was cut out from the above-obtained positive electrode.
  • a measurement negative electrode having a size of 36 mmx36 mm was cut out from the above-obtained negative electrode.
  • the measurement positive electrode and the measurement negative electrode were laminated with a separator interposed therebetween to prepare an electrode group. This electrode group was inserted into a laminate external body, and the nonaqueous electrolytic solution was injected thereinto. Next, an opening was sealed by thermal welding. As a result, a laminate battery having a rated capacity of 20 mAh was prepared.
  • the positive electrode mixture layer contained the first layer (upper layer) and the second layer (lower layer); the ratio of the volume of the first layer to the volume of the positive electrode mixture layer was 20 vol% to 75 vol%; the first layer contained LFP and NCM; the ratio of the mass of LFP to the total mass of LFP and NCM in the first layer was more than 0 mass% and 80 mass% or less; the second layer contained NCM; and the ratio of the mass of LFP to the total mass of the positive electrode active material in the positive electrode mixture layer was 7.5 mass% to 20 mass%.
  • the batteries Al to A9 (Examples) were compared to the batteries Bl to B14 (Comparative Examples) which did not satisfy the above-described conditions, the output in a low SOC was high, and the amount of gas produced during overcharge increased.
  • Batteries Bl and B2 (Comparative Examples) In the batteries Bl and B2 in which the entire positive electrode mixture layer was configured as the NCM single layer, the output in a low SOC was not sufficient. In addition, the amount of gas produced during overcharge was small. Further, it was found from the results of the battery B2 that, in the NCM single layer, when the mixture density increases, the amount of gas produced during overcharge decreases.
  • the output in a low SOC was improved by the mixing of LFP.
  • the filling factor of the positive electrode mixture layer was improved by the mixing of LFP.
  • the batteries B3 was compared to the batteries Al and A2
  • the ratios of the mass of LFP to the total mass of the positive electrode active material were the same.
  • the amounts of gas produced during overcharge were significantly different from each other. That is, in the batteries Al and A2 in which LFP was biasedly present in the upper layer (first layer) of the positive electrode mixture layer, the amount of gas produced significantly increased. The reason is presumed to be that, since LFP having high resistance was biasedly present in the upper layer, the polarizations were likely to occur, an increase in the potential of the upper layer became significant, and the gas production reaction was accelerated.
  • the ratio of the mass of LFP to the mass of the positive electrode active material in the first layer was 80 mass%, superior battery performance was obtained.
  • the mass ratio of LFP in the first layer was increased to be more than 80 mass%, the same results as those of the battery Bl l may be triggered. Accordingly, the ratio of the mass of LFP to the mass of the positive electrode active material in the first layer is required to be 80 mass% or less.
  • the volume ratio of the first layer When the volume ratio of the first layer was less than 20 vol%, the amount of gas produced during overcharge decreased. The reason is presumed to be that portions where the polarizations occurred were not able to be sufficiently secured. Accordingly, the volume ratio of the first layer is required to be 20 vol% or more.
  • the effects of the physical properties of lithium iron phosphate powder on battery performance were examined. Specifically, the following batteries A10 to A15 were prepared to evaluate the output in a low SOC, the amount of gas produced during overcharge, and charging-discharging cycle characteristics thereof using the same method as described above. Here, the batteries A10 to A13, and A15 correspond to Examples.
  • LFP (b) was obtained using the same method as that of LFP (a), except that the firing temperature was changed to 600°C.
  • LFP (c) was obtained using the same method as that of LFP (d), except that the firing temperature was changed to 550°C.
  • LFP (e) was obtained using the same method as that of LFP (d), except that the firing temperature was changed to 650°C.
  • LFP (f) was obtained using the same method as that of LFP (d), except that the firing temperature was changed to 500°C.
  • the physical properties of each LFP powder obtained as described above were measured using a laser diffraction scattering particle size distribution analyzer "Microtorac MT 3000 ⁇ " (manufactured by Nikkiso Co., Ltd.) and "Macsorb HM model-1201" (manufactured by Mountech Co., Ltd.) The results are shown in Table 3 of FIG 9.
  • batteries A10 to A15 were prepared with the same method as that of the above-described battery Al .
  • the configurations of the positive electrode mixture layers are shown in Table 4 of FIG 10.
  • the numeral values shown in the item "BET Specific Surface Area" of Table 4 of FIG. 10 are the BET specific surface areas of the positive electrode mixture used for forming the first layer.
  • the numerical values shown in the item "Maximum Pore Size” were measured as follows. First, three measurement samples having a size of 200 mmx55 mm were cut out from the positive electrode used in each battery. In order to collect the measurement samples, the positive electrode was equally divided into three regions having the same area in the longitudinal direction, and one measurement sample was collected from each region. Next, using a pore distribution measuring device (for example, "Autopore IV 9500” manufactured by Shimadzu Corporation), the maximum pore sizes of the respective measurement samples were measured. The numerical values shown in Table 4 of FIG. 10 were obtained based on the arithmetic average of the maximum pore sizes. It was found from Table 4 of FIG.
  • the maximum pore size measured as described reflects the pore distribution of the first layer, that is, the maximum pore size of the first layer.
  • the maximum pore sizes measured using the same method were 0.5 ⁇ to 0.7 ⁇ .
  • the amount of gas produced increased because the nonaqueous electrolytic solution easily penetrated into the first layer through pores, and the produced gas were easily discharged through the pores.
  • the maximum pore size of the positive electrode mixture layer (first layer) is required to be 0.70 ⁇ or less.
  • LFP is preferably 8.6 m 2 /g to 13.2 m 2 /g, more preferably 8.6 m 2 /g to 11.6 m 2 /g and still more preferably 8.6 m /g to 9.5 m 2 /g.

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Abstract

L'invention porte sur une couche de mélange d'électrode positive (12) qui comprend une première couche (12a) qui présente une surface principale MS et une seconde couche (12b) formée plus proche du côté du collecteur de courant d'électrode positive (11) que la première couche (12a). Un rapport du volume de la première couche (12a) sur le volume de la couche de mélange d'électrode positive (12) est de 20 à 75 % en volume. La première couche (12a) contient du phosphate fer lithium (LFP) (1) et un oxyde composite de manganèse cobalt nickel lithium (NCM) (2). Un rapport de la masse du LFP (1) sur la masse totale du LFP (1) et du NCM (2) dans la première couche (12a) est supérieur à 0 et de 80 % en masse ou moins. La seconde couche (12b) contient du NCM (2). Un rapport de la masse du LFP (1) sur la masse totale du matériau actif d'électrode positive dans la couche de mélange d'électrode positive (12) est de 7,5 à 20 % en masse. Une taille de pore maximale de la première couche (12a) est de 0,50 à 0,70 µm.
PCT/IB2015/001493 2014-09-08 2015-09-02 Batterie rechargeable à électrolyte non aqueux WO2016038438A1 (fr)

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DE112015004095.1T DE112015004095T5 (de) 2014-09-08 2015-09-02 Sekundärbatterie mit nichtwässrigem elektrolyten
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EP3451421A4 (fr) * 2016-06-14 2019-07-31 LG Chem, Ltd. Électrode pour batterie secondaire et batterie secondaire au lithium comprenant celle-ci
US11228038B2 (en) 2016-06-30 2022-01-18 HYDRO-QUéBEC Electrode materials and processes for their preparation

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